The invention relates generally to crop harvesters and, more specifically, to a corn stalk strength measuring device mounted on a harvester for harvesting corn and methods for measuring corn stalk strength.
Stalk lodging in corn is the breakage of the corn stalk below the ear. Stalk lodging in corn results in increased harvest losses, slower harvest equipment speeds, increased drying cost and in most cases, a significant volunteer problem the following season. Yield losses from stalk lodging range from 5 to 25 percent nationwide. Root and stalk lodging are some of the most important traits in commercial maize breeding.
Causes of stalk lodging include the following. Plant population levels that are too high decrease the amount of light in the crop canopy and cause the corn plants to become tall and thin. The physical strength of the corn stalk under these conditions is significantly reduced. In addition, plant-to-plant competition for light, nutrients, and water enhances the competition for carbohydrates between the stalk and ear within the plant, thus reducing the vigor of the cells in the stalk and predisposing them to invasion by stalk rot. Extremes in soil moisture can increase the occurrence of stalk lodging. Excessive soil moisture retards root growth and development, leading to a less than optimum root system which cannot adequately support plant growth. On the other hand, droughty conditions stress the crop and enhance the development of stalk rot by reducing movement of sugars to the root system. Nutrient imbalances and/or deficiencies predispose corn plants to stalk rot and stalk lodging. For example, high nitrogen fertility levels coupled with low potassium levels enhance the potential for stalk rot. High nitrogen levels enhance lush vegetative growth, while low potassium levels increase the amount of premature stalk death. Together, these conditions produce an ideal situation for stalk rot and lodging. Conversely, low levels of soil nitrogen may result in less vigorous plants which put all their available energy into producing grain. This leaves the stalk vulnerable to stalk rot organisms and, ultimately, stalk lodging. Damage caused by the corn rootworm and the European corn borer can predispose the corn plant to invasion by stalk rotting organisms, as well as lead to outright yield loss. Corn rootworm larvae decrease the amount of water and nutrient uptake by feeding on the roots, whereas the European corn borer damages the stalk by feeding on the pith and the vascular tissue. In either situation, the corn plant is placed under physiological stress, which favors both stalk rot development and stalk lodging. These insects can also encourage the development of stalk rots by reducing the photosynthetic area of the plant, causing wounds through which pathogens enter stalks and roots, and carrying disease inoculum into tissues. Cultural practices which increase the amount of disease or insect pressure can also increase the amount of lodging that occurs in the corn crop. Leaving disease-infected corn stubble on the soil surface through reduced tillage methods can increase the incidence of stalk rot and stalk lodging in monoculture. Continuous cropping of corn also enhances the potential for insect problems such as European corn borer and corn rootworm.
One of the approaches to preventing stalk lodging is the development of commercial hybrid seed varieties with improved stalk strength. Currently, corn development programs commonly include selection of new corn varieties for advancement based at least in part on stalk strength. Stalk strength measurements can be taken of plants of the corn varieties at various times throughout the growing season, however, the most common practice is to count or estimate broken plants prior to harvest. Good expression of the stalk strength trait depends upon winds that are strong enough to break weak plants yet not so severe as to cause widespread, indiscriminant lodging on all plots. Instruments have been developed which measure resistance to penetration of the stalk. Since a person must walk through the plot of growing corn, conduct the measurement using the hand tool and record the measurement for each plant, it is a time-consuming and labor intensive process that can only be performed on a relatively small number of plots. There is a need, accordingly, for an automated apparatus and improved methods for taking stalk strength measurements on a large number of plots.